This invention relates to a method of accurately and dynamically estimating the concentration of recirculated exhaust gases in the gas entering the combustion chamber of an internal combustion engine equipped with an exhaust gas recirculation (EGR) system.
Recirculation of a controlled amount of exhaust gas into the intake air stream of an internal combustion engine, via EGR valve control and/or valve overlap control, has been effectively utilized for improving exhaust gas emissions and fuel economy. Specifically, the recirculated exhaust gas tends to reduce the peak combustion temperature and pressure, which in turn, reduces nitrogen oxide components (NOx) in the exhaust. Fuel economy improvements occur because the recirculated exhaust gases raise the intake manifold pressure, reducing engine pumping losses. On the other hand, reduced combustion stability and degraded engine performance can occur if the EGR concentration is too high. Thus, it is necessary to have a reliable estimation of the EGR concentration of the gas entering the combustion chamber if the advantages of EGR are to be fully realized without also incurring the disadvantages. Steady state estimations of the EGR concentration can be readily obtained, but what is needed is a continuously reliable estimation of the EGR concentration. The need is especially great in direct injection gasoline engines where the controller initiates large changes in EGR concentration when changing combustion modes.
The present invention is directed to an improved method of dynamically estimating the concentration of recirculated exhaust gases entering the combustion chambers of an internal combustion engine equipped with an exhaust gas recirculation (EGR) system. According to the invention, the EGR concentration at the engine intake ports is separately estimated based on a dynamic model of air and exhaust gas mixing in the engine, and the EGR concentration for control purposes is determined by adjusting the result of the dynamic model based its deviation from an estimate of the EGR concentration based on a conventional steady-state model. This method provides the total EGR concentration, but can alternatively provide the inert EGR concentration through the inclusion of an exhaust inert ratio model.